This invention relates to a process for preparing certain titanium and zirconium complexes comprising a single, cyclic, delocalized n-bonded ligand group wherein the metal of said complexes is in the +2 formal oxidation state. More particularly, this invention relates to such processes wherein the metal is covalently bonded to the cyclic group via the delocalized n-system and also covalently bonded thereto via a divalent ligand group. Such complexes are referred to in the art as "constrained geometry" complexes.
The preparation and characterization of certain biscyclopentadienyl zirconium and hafnium diene complexes are described in the following references: Yasuda, et al., Organometallics, 1, 388 (1982) (Yasuda I); Yasuda, et al., Acc. Chem. Res., 18, 120 (1985), (Yasuda II); Erker, et al., Adv. Organomet. Chem., 24, 1 (1985); and U.S. Pat. No. 5,198,401. The preparation of certain Ti, Zr, and Hf monocyclopentadienyl diene complexes lacking the present bridged ligand structure, was described in Yamamoto et al., Organometallics, 8, 105 (1989) (Yamamoto) and Blenkers, J, et al., Organometallics, 6, 459 (1987).
Constrained geometry metal complexes, including titanium complexes, and methods for their preparation are disclosed in U.S. application Ser. No. 545,403, filed Jul. 3, 1990 (EP-A-416,815); U.S. application Ser. No. 547,718, filed Jul. 3, 1990 (EP-A-468,651); U.S. application Ser. No. 702,475, filed May 20, 1991 (EP-A-514,828); U.S. application Ser. No. 876,268, filed May 1, 1992, (EP-A-520,732) and U.S. application Ser. No. 8,003, filed Jan. 21, 1993 (WO93/19104), as well as U.S. Pat. No. 5,055,438, U.S. Pat. No. 5,057,475, U.S. Pat. No. 5,096,867, U.S. Pat. No. 5,064,802 and U.S. Pat. No. 5,132,380.